Piezoelectric materials, are generally ABO3-type perovskite-type metal oxides such as lead zirconate titanate (hereinafter referred to as “PZT”). However, PZT contains lead coordinating at an A-site of a perovskite unit cell. Therefore, the adverse effect of a lead component on the environments is considered as a problem. In order to comply with the problem, a lead-free piezoelectric material and piezoelectric element using a perovskite-type metal oxide are proposed.
Barium titanate (BaTiO3) and derivatives thereof are known as piezoelectric materials composed of lead-tree perovskite oxides. Patent Literature 1 discloses a piezoelectric material in which A-sites of barium titanate are partially substituted by calcium (Ca) and B-sites are partially substituted by manganese (Mn), iron (Fe), or copper (Cu). Patent Literature 1 discloses a piezoelectric material and piezoelectric element which are improved in temperature stability of piezoelectric characteristics near room temperature and mechanical quality factor. Improvement in the mechanical quality factor has the effect of decreasing the heat generated during drive of a piezoelectric element and power consumption. However, the piezoelectric material disclosed in Patent Literature 1 has the problem that the piezoelectric characteristics are degraded as compared with barium titanate unsubstituted by an element such as Ca or the like.
As another example, Patent Literature 2 and Non-Patent Literature 1 disclose piezoelectric materials in which A-sites of barium titanate are partially substituted by calcium (Ca) and B-sites are partially substituted by zirconium (Zr) to improve piezoelectric characteristics. The piezoelectric materials have a low Curie point of as low as 80° C. or less and have the problem of degrading the piezoelectric characteristics due to depolarization in a high-temperature environment in a vehicle in the summer. The piezoelectric characteristics of piezoelectric elements undergoing polarization are generally degraded by depolarization at a temperature 10° C. to 20° C. lower than the Curie temperature. Also, the piezoelectric materials disclosed in Patent Literature 2 have a low mechanical quality factor.